Reversible Diels-Alder based polymers are generally known, and have been investigated for use in solid ink printing. These are disclosed, for example, in U.S. Pat. Nos. 5,844,020, 5,952,402, and 6,042,227. These reversible Diels-Alder based polymers would be particularly useful in ink jet applications, because the ink jet apparatus allows for precise, imagewise control of the placement of material, and thus would allow for the production of precise, hard polymer films possessing the reversible adhesion and solid-to-liquid conversion properties.
However, the Diels-Alder based polymers previously investigated suffered from long solidification times after being deposited on a substrate. For example, it was found that many of the prior Diels-Alder based polymers had solidification times on the order of several hours, making them unsuitable for use in most printing applications. Long solidification times are unsuitable in most printing applications because while the printed material remains in a liquid or semi-liquid state, the image can become distorted, image quality can degrade, and the printed images cannot be stacked on top of each other resulting in either large space needs or low throughput.
Accordingly, there is a need for improved materials that exhibit the reversible polymerization property, but that have shorter solidification times to permit their efficient and economical use in commercial processes.
A wide variety of adhesive materials are also known, including epoxy-based adhesives, acrylate-based adhesives, and the like. Such materials have been shown to provide very strong bonding properties. However, many of these adhesive materials are irreversible. That is, the objects that are bonded together cannot be easily separated or separated without damage or destruction to the objects.
The concept of reversible adhesives has been previously described. For example, one such reversible adhesive system is described in Luo, X. et al., Polymer 2010, 51, 1169-75; Aubert, J. H., J. Adhesion 2003, 79, 609-616; Wouters, M. et al., Prog. Org. Coatings 2011, 72, 152-158; and U.S. Pat. No. 6,825,315, the entire disclosures of which are incorporated herein by reference. The described system uses a combination of epoxy or acrylate materials and Diels-Alder materials.
In the systems described, irreversible epoxy or acrylate chemistry is used as the adhesion force, while the Diels-Alder chemistry only provides the means for reversibility. Because the Diels-Alder materials are present, heating and cooling of the substrate will result in delamination or re-adhesion. However, in these examples the surface is irreversibly altered once the epoxy groups are affixed. Total restoration or cleaning of the surface would require mechanical removal of the epoxy residue, which could possibly damage the substrate, and more importantly would prevent re-adherence of the materials.
Thus, there remains a need in the art for improved adhesives that allow for reversible adhesive of objects, yet without any permanent alteration or damage to the objects being adhered.